In article , Eric R Snow
wrote:

About a year and a half ago I had a guy ask if I could weld repair his
favorite wheelchair. I told him to bring it by and I'd look at it. It
was some kind of mystery metal that was magnetic. I ended up tig
welding it with stainless because I've found SS would often make a
better repair than 70S2 when the iron alloy is unknown but not likely
to be tool steel. My policy on these types of repairs is to guarantee
my weld but not the edge of the HAZ and beyond. So, if the weld
breaks, or if the bead breaks out of the part, I fix it for free.
Forever. But if it breaks beyond the weld then it's tough beans. It's
hard to tell where the HAZ ends sometimes so I figure about .060"
beyond the bead is where the guarantee ends. Anyway, all this was
explained to the wheelchair owner and he said sure, weld it up. Then,
I get a call this morning from the guy. He asks if I remember the job
and I say yeah. He says it's still holding and thanks for the good job
done. Boy, did that make my day!
Eric R Snow,
E T Precision Machine


Likely it was 4130.
A lot of wheelchairs are made of it.

Wheelchair engineering follows bike frame engineering, just a little
heavier.

Be careful using SS as a filler on chrome moly or in any location that
will endure a lot of flex.
SS is very strong and is excellent for getting a clean weld on dubious
metal, but SS also has less ability to withstand repeated flexing.

It tends to stress fracture and then tear out.

So when welding SS you have to make sure the welds will be better
triangulated and braced than with steel.

It is for this reason that a SS bike frame would be a huge mistake.

I prefer the Aerospace alloys that are nickle based as filler metals
for unknown base metals.
They tend not to stress fracture as quickly as SS and are even better
at dealing with dirty or oxidized base metal.

Hastelooy W and Inconel 625 are my favorites.